The Optus 4G TD-LTE Trial: Everything You Need To Know

Optus today officially began trials of its TD-LTE 4G service in Canberra, ahead of a public launch for the service on June 4. Here's what's happening and how it will potentially make 4G more reliable.

Optus has offered 4G services since mid-2012, using FD-LTE technologies in the 1800MHz spectrum. The new trial, which will commence with 12 base stations in Canberra today, uses TD-LTE spectrum in the 2300MHz band. Optus also has two trial base stations in Sydney.

What's the difference between the two approaches? With FD-LTE (also sometimes known as 'paired spectrum), separate area of spectrum are used for uploads and downloads. With TD-LTE (sometimes known as 'unpaid spectrum'), the same spectrum is used for both, but at different times. For Optus' network, the ratio of download:upload allocation is 3:1.

What speeds will that offer? The theoretical upper limit is 70Mb/second (some TD-LTE networks claim higher speeds, but that depends on how the timeslots are allocated). In practice, Optus says 61Mb/second is the highest speed seen on the network.

Optus will initially offer two devices that can use the TD-LTE network: a USB modem which will only be on sale in Canberra, and a Wi-Fi hotspot that will be on sale everywhere. The latter will include support for both TD-LTE and FD-LTE, switching to whichever network is available. Pricing hasn't yet been announced.

In the long term, Optus also expects handsets that can use TD-LTE will be made available. "We are really confident that the TD-LTE ecosystem has developed to where it's ready to launch services," said Optus MD of networks Guenther Ottendorfer.

Optus claims that by mid-2014, its 4G network will be accessible to 70 per cent of the metro population, while its 3G network will cover 98 per cent. 4G currently operates in Sydney, Melbourne, Brisbane, Perth and Adelaide (mostly within CBD areas), as well as parts of the Gold Coast, Coffs Harbour, Newcastle, Toowoomba and Byron Bay.

I wouldn't worry too much about fragmentation. Telstra and Optus are adopting largely the same frequencies (700, 1800, 2600). There are only a few exclusive LTE frequencies - 900 MHz & 2100 MHz (Telstra) and 2300 MHz (Optus), but this is just like 3G scene is (850 MHz and 900 MHz).

It will be interesting to see how chip manufacturers cope. Essentially they have to, there simply isn't enough spectrum to rely on one or few bands.